The present invention relates to a direct current motor provided with a stator having four or more magnetic poles.
The direct current motor disclosed in Japanese Laid-Open Patent Publication 2004-88915 has a stator where magnets are placed to form four or more magnetic poles. The rotary shaft rotates integrally with an armature core and a commutator core, and the armature core has a plurality of coils. The commutator has a plurality of segments arranged in the circumferential direction, and a short-circuit conductor for short-circuiting predetermined segments to each other. The coils are each connected to corresponding segments such that one closed circuit (closed loop) including the short-circuit conductor and all of the coils is formed between an anode brush and a cathode brush which contact and slide against the segments.
In the direct current motor in the above described publication, however, the number of closed loops including the short-circuit conductor and all of the coils is one. Therefore, it is necessary for the cross-sectional area of the short-circuit conductor to be large, in order to prevent the density of the main current flowing through the short-circuit conductor from becoming too high. As a result, the space in which the short-circuit conductor is placed becomes large, making the commutator and the direct current motor large. In the case where the short-circuit conductor is short-circuit wires made of conducting wire, for example, it is necessary for the space between the commutator where short-circuit wires are placed and the armature core in the axial direction to be set large. In addition, in the case where the short-circuit conductor is a great number of short-circuit pieces formed through punching out a conductor plate, the commutator having these short-circuit pieces becomes large.